Phosphorus concentrations in surface runoff and subsurface flow from agricultural catchments by the Yuqiao Reservoir
于桥水库周边农业小流域地表径流和亚表层流的磷素流失浓度特征

Afield study on phosphorus loss characteristics was conducted over 5 years in two agricultural catchments by the Yuqiao Reservoir,the drinking water source area for Tianjin City.Total phosphorus concentration(TP) in the surface runoff of orchards was the highest among five kinds of land uses(mean concentration above 10 mg·L-1),that of village was the second highest and that of cropland was the lowest at a level of about 3 mg·L-1.The phosphorus concentration in subsurface flow of orchards was the highest,that of vegetable gardens was the second,and that of cropland was the lowest.TPin surface runoff at the outlet of the Taohuasi catchment amounted to 10.07 mg·L-1,while that of the Caogezhuang catchment was 0.69 mg·L-1.Different landscape spatial patterns and water transport pathways were responsible for this gap.The short distance(about 200 m) between the village and the receiving water and the "road" type transport pathway in the Caogezhuang catchment increased the nutrient discharge load.The longer distance(about 1500 m) from the village and orchard in the Taohuasi catchment to the receiving water increased the phosphorus transport pathway.And small stone dams,a vegetated filter strip and dry ponds within the ephemeral stream could retain nutrients in the Taohuasi catchment.